Why is it impossible to find a diesel operated auxiliary water heater like an Eberspaecher or Webasto in the US. Are they illegal for some reason? In my opinion there's nothing better you can do to your car in the winter, and it's comfy! I have a gasoline operated auxiliary air heater in my vanagon, so why are there no aux water heaters?

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'99 S420, 155k
'91 VW Vanagon GL, 150k
'85 VW Vanagon GL, 120k
'82 VW Westy, aircooled, 165k